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From "lvh (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-11637) Immutable-friendly read consistency level
Date Sat, 23 Apr 2016 23:09:12 GMT
lvh created CASSANDRA-11637:
-------------------------------

             Summary: Immutable-friendly read consistency level 
                 Key: CASSANDRA-11637
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11637
             Project: Cassandra
          Issue Type: New Feature
            Reporter: lvh
            Priority: Minor


Many Cassandra applications use immutable, append-only models. For those models, you can accept
read consistency {{ONE}}, since the data either exists (and then it's the data you want) or
it doesn't. However, it's possible that the data hasn't made it to that node yet, so "missing"
data might mean "actually missing" or "not here".

Riak has a convenient read consistency option for this, called notfound_ok (default true).
When false, the first succeeding read will succeed the operation (a la consistency level {{ONE}}),
but a missing read from any node will keep trying up to the normal consistency level (e.g.
{{QUORUM}}).

The workaround for this is for applications to implement an "UpgradingConsistencyPolicy" (dual
to DowngradingConsistencyPolicy) that tries e.g. {{QUORUM}} after {{ONE}} fails, and then
writes with e.g. {{QUORUM}}.

This is related to CASSANDRA-9779; but it seems that ticket only explores the compaction/collation/materialized
view angle, not the fast & safe read consistency angle.

Thanks to [~jjirsa]] for helping me dig through this, find the related ticket, and confirm
Cassandra currently does not support this.



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